The purpose of the proposed set of studies is to explore language impaired preschoolers' word acquisition processes. Earlier studies indicate that normal preschool children have a robust ability to "fast map" new word meanings, to arrive at a partial understanding based on few experiences with a new word. In contrast, pilot work suggest that LI children have limited fast mapping ability. Possible reasons why LI children are unable to do this include: (a) limited linguistic processing skills, (b) limited general linguistic knowledge, or (c) limited vocabulary. It is hypothesized that LI children's relatively limited vocabularies are a consequence of an inability to rapidly process incoming lingusitic information, to detect linguistic patterns, compare with their own lexicon, and quickly assign a tentative meaning to a word. The set of studies is designed to test the hypothesis against the other alternatives, by comparing LI preschoolers with age and language matched normal peers, statistically controlling for vocabularly levels. The studies explore four areas: (1) the best means of measurement (pictures versus video); (2) LI children's ability to process new words "online" in naturalistic circumstances, as a function of consistency of grammatical context, frequency of exemplars, or the ratio of familiar/unfamiliar; (3) LI children's ability to fast map when the input is focused, as a function of added pauses or additional verbal labelling; and (4) the breadth or depth of LI children's word learning (range of exemplars and generalization from comprehension to production). Video materials will be develoepd and used as stimuli. The results will add to our knowledge of linguistic processing capabilities of LI preschoolers, in the domain of word acquisition. Outcomes will include principles for training word meaning and guidelines for preparation of appropriate video tutorial materials.